A proposal by the junta for a single internet gateway to allow authorities to monitor content would destroy competition, while being reminiscent of the most authoritarian measures to stifle free speech, a former information minister said on Thursday.
The plan to create a single gateway for all internet traffic was approved by the military government in August but details remain unclear.
Free-speech activists say the gateway, referred to as a China-style "Great Firewall", is the latest effort by the junta to smother dissent and monitor detractors.
The plan has also triggered concern that internet speeds would plummet, which would almost certainly hurt online business and anger internet users.
"Once it becomes a single gateway there will be a problem with traffic speeds," said Anudith Nakornthap, a former information minister under the government of ousted Prime Minister Yingluck Shinawatra.
"The junta wants to control various websites. This is similar to the control mechanisms of non-democratic countries such as China and North Korea."
The military has ruled with a strict hand since taking over the administration of the country last year, banning protests and not tolerating dissent, and has shut down thousands of websites.
Thailand has 10 internet gateways run by private and state-owned companies. The one-gateway plan, according to observers, would merge traffic through one state-run firm.
Prasong Ruangsirikulchai, executive director of the Telecommunications Association of Thailand, said the government would meet fierce opposition from private firms that would be forced to suspend their lines.
"If the government is not strong it will not be able to achieve this," Mr Prasong said during a talk at the Foreign Correspondents Club of Thailand on Wednesday.
"They will have a tough time convincing private companies to cut their lines."
The military has said the plan is necessary for national security, but Prime Minister Prayut Chan-ocha told reporters on Thursday it would not go ahead if it violated rights.
"If it violates rights, we can't do it," he said.
Critics say the plan goes against a digital-economy master plan to encourage online business by attracting investment from companies like Facebook Inc, which opened its first Thai office last month.
The government played down a coordinated attack last week on several state websites in a protest against the plan.
